Question

Given X ~ B(n, p) if p = 0.6 and E(X) = 6, find n and Var(X). 

Answer 1

Given: p = 0.6 and E(X) = 6

E(X) = np

∴ 6 = n × 0.6

n = `6/0.6`

n = 10

Now, q = 1 – p

= 1 – 0.6

= 0.4

∴ Var(X) = npq

= 10 × 0.6 × 0.4

= 2.4

Hence, n = 10, Var(X) = 2.4